Your suggestion is that a templating JIT that just drops in some machine code that matches the method, doing no optimization, would get all the win. Such a compiler is indeed much faster than an interpreter, but it's nowhere close to an optimizing compiler. Mike Pall, the author of LuaJIT, would be very surprised if you suggested that his compiler performed similarly to something simple like that.
Your suggestion is that a templating JIT that just drops in some machine code that matches the method, doing no optimization, would get all the win. Such a compiler is indeed much faster than an interpreter, but it's nowhere close to an optimizing compiler. Mike Pall, the author of LuaJIT, would be very surprised if you suggested that his compiler performed similarly to something simple like that.